The particular mechanisms underlying the sub-second control of dopamine release by glutamate and other neurotransmitters/neuromodulators are not well-known largely because the analytical methodology required to address these important questions has not been sufficiently developed. Although one technique, fast-scan cyclic voltammetry at carbon-fiber microelectrodes, offers sufficient temporal resolution to measure the release and uptake of electroactive biogenic amines such as dopamine, its use in characterizing such sub-second neurotransmitter/neuromodulator interactions is lacking. This deficiency represents a serious roadblock because signaling events in the brain that influence outward physical responses and cognitive events occur within this sub-second time regime. Therefore, the central aim of the proposed research is to develop and apply tools that will allow for the quantitative study of these neurotransmitter interactions in living tissues and in vivo. To temporally-compatible methods, fast-scan cyclic voltammetry and the photoactivation of the p- hydroxyphenyl caged form of glutamate (pHP-Glu), used here as a model caged system, will be applied to measure the sub-second response of dopamine release in response to millisecond timescale exposures to exogenous glutamate. The overall objective of this proposed research will be accomplished by successfully completing two specific aims: (1) Develop and validate an electrochemical method to quantitatively measure dopamine release and photoactivated glutamate simultaneously and (2) Optimize the construction and use of a combined photoactivation probe/carbon-fiber microelectrode for measuring the impact of caged compound photoactivation on dopamine release events in vivo. This approach is innovative because it is among the first to simultaneously apply these two high temporal resolution techniques in living tissues and animals. The development and application of this proposed methodology is significant because it will enable laboratory researchers to measure sub-second timescale dopamine release in response to ms-timescale glutamate application. Moreover, this work should have a broad impact since the application of these techniques can be expanded to include the detection of other electroactive neurotransmitters and neuromodulators, such as serotonin, hydrogen peroxide (H2O2), and nitric oxide (NO), and the photoactivation of other bioactive molecules, such as GABA and specifically designed synthetic agonists/antagonists. Importantly, this research directly relates to the NIH mission of seeking fundamental knowledge about the nature and behavior of living systems and reducing the burdens of illness and disability in that applies to, but is not limited to: (1) fundamental neurobiological studies; (2) studies of dopamine-related movement disorders [e.g. Huntington's disease (HD), Parkinson's disease (PD), Tourette's syndrome (TS)]; (3) studies of addiction and depression; and (4) studies addressing the mechanisms of action of CNS-active pharmacological agents.